/**
 * Copyright (C) 2006 Google Inc.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package com.google.inject.internal;

import com.google.inject.internal.InjectorImpl.InjectorOptions;

import java.lang.reflect.Proxy;
import java.util.ArrayList;
import java.util.List;

/**
 * Context of a dependency construction. Used to manage circular references.
 *
 * @author crazybob@google.com (Bob Lee)
 */
final class ConstructionContext<T> {

    T currentReference;
    boolean constructing;

    List<DelegatingInvocationHandler<T>> invocationHandlers;

    public T getCurrentReference() {
        return currentReference;
    }

    public void removeCurrentReference() {
        this.currentReference = null;
    }

    public void setCurrentReference(T currentReference) {
        this.currentReference = currentReference;
    }

    public boolean isConstructing() {
        return constructing;
    }

    public void startConstruction() {
        this.constructing = true;
    }

    public void finishConstruction() {
        this.constructing = false;
        invocationHandlers = null;
    }

    public Object createProxy(Errors errors, InjectorOptions injectorOptions, Class<?> expectedType) throws ErrorsException {
        if (injectorOptions.disableCircularProxies) {
            throw errors.circularProxiesDisabled(expectedType).toException();
        }
        if (!expectedType.isInterface()) {
            throw errors.cannotSatisfyCircularDependency(expectedType).toException();
        }

        if (invocationHandlers == null) {
            invocationHandlers = new ArrayList<DelegatingInvocationHandler<T>>();
        }

        DelegatingInvocationHandler<T> invocationHandler = new DelegatingInvocationHandler<T>();
        invocationHandlers.add(invocationHandler);

        // TODO: if I create a proxy which implements all the interfaces of
        // the implementation type, I'll be able to get away with one proxy
        // instance (as opposed to one per caller).
        ClassLoader classLoader = BytecodeGen.getClassLoader(expectedType);
        return expectedType.cast(Proxy.newProxyInstance(classLoader, new Class[] { expectedType, CircularDependencyProxy.class }, invocationHandler));
    }

    public void setProxyDelegates(T delegate) {
        if (invocationHandlers != null) {
            for (DelegatingInvocationHandler<T> handler : invocationHandlers) {
                handler.setDelegate(delegate);
            }
            // initialization of each handler can happen no more than once
            invocationHandlers = null;
        }
    }
}
